1. Field of the Invention
This invention relates to a method for patterning a film, inclusive of steps of exposing and developing a resist, and a method for exposing resist film.
2. Description of the Prior Art
The process of manufacturing a semiconductor device comprises a step of patterning a film formed of a semiconductor, a conductor, or an insulator. The patterning of this film is generally accomplished by masking a substrate with a resist and etching the part of the substrate that is left uncovered with the mask.
The production of a mask from a resist proceeds from a step of spreading the resist on a film, then through a step of exposing the resist thereby forming a latent image thereon, and subsequently to a step of developing the resist thereby visualizing the latent image.
For the exposure, a method which resides in irradiating the resist with an ionizing radiation is generally adopted. The term "ionizing radiation" refers to such a concept as embraces not only such lights as ultraviolet light and i light but also such beams of charged particles as electron beams and ion beams. As the resist, a material which proves to be appropriate for the kind of ionizing radiation adopted for the exposure is selected.
An electron beam (EB) resist is used when an electron beam is adopted for the exposure. The patterning of the EB resist is carried out as follows.
First, as illustrated in FIG. 1A, a lower insulating film 102, a wiring 103, and an upper insulating film 104 are formed on a semiconducting substrate 101 and a positive electron beam resist 105 is spread on the upper insulating film 104. Thereafter, the electron beam resist 105 is irradiated with an electron beam to form a latent image on the electron beam resist 105.
Next, the electron beam resist 105 is developed to form a pattern therein as illustrated in FIG. 1B.
Thereafter, the upper insulating film 104 is etched, with the resist pattern as a mask.
The patterning of the insulating film is presumed, for example, to shape a dielectric film such as a capacitor and form a contact hole in an interlayer insulating film.
When the exposure of the electron beam resist 105 is effected by the use of an electron beam as described above, the negative charge which passes through the electron beam resist 105 accumulates in the insulating film and the electron beam which is subsequently used for the exposure inevitably spreads in the lateral direction under the influence of the Coulomb force as illustrated in FIG. 11. The consequence is the disadvantage that the area of exposure of the electron beam will be substantially dilated.
Further, the electron beam resist offers low resistance to such dry etchings as reactive ion etching (RIE) and ion milling as compared with the resist of the quality proper for exposure to such lights as i light and ultraviolet light. When the insulating film to be patterned is formed of a material slow in etching, the practice of applying an electron beam resist in a large thickness is generally followed.
When the electron beam resist is applied in a layer large in thickness, however, the increase of the thickness augments proportionately the expansion of electrons and inevitably adds to the width of pattern of the latent image to be formed in the electron beam resist and renders it difficult to improve the pattern in fineness.
The problem just mentioned arises likewise when the resist is to be patterned by the use of a cation beam.